You have up to seven encounters with the miners throughout the game, with a possibility of taking twenty-four photos in total. Even though the descriptions state that the photographs should be taken while the target is in motion, shots of stationary ones are also counted. For moving targets, timely and rapid shooting is needed to reach the number of valid shots stated in parantheses below.
1) Depth 2, one can be seen wandering behind the trees. (5 shots)
2) Depth 3, one appears right in front of you after picking up the gas can. (1 shot)
As you approach him, another one spawns behind him and rushes at you. (4 shots)
3) Depth 3 to 4, one can be found staring as you descend to the fourth level. (1 shot)
4) Depth 4, another miner rushes at you as you make your way to the 'device'. (2 shots)
(This one may not appear at all, depending on the route taken.)
5) Depth 4, one can be found standing guard with a needed key in hand. (1 shot)
6) Depth 5, another miner spawns behind and rushes at as you open the first (unmarked) door right behind the one with a hand-written warning on it. (8 shots)
7) Depth 5, you come across three doors labeled 0, 8 and 16, respectively. They are tied to the number of your valid shots up to this point - i.e., as long as you have sixteen shots, it is possible to open all three of them, yet opening one locks you out of the other two. Although the paths on offer differ slightly, all of them has a miner rushing at you. (2 shots) (16 is the fastest route).

Right after the first encounter with a miner in Depth 2, you come across an opening in the cave system with a pit in the middle. Drop down into the said pit. Note that this does not result in a death. In fact, it is the preferable way for descending as it is faster and leads to more collectibles than the other paths available at this point.
You find a cave-in with a detonator nearby as you explore Depth 4. Pick up the detonator, place three sticks of dynamite on the box and follow the on-screen instructions to detonate them. Check the place after the detonation to find the axe. Mind that not picking up the axe locks you out of another achievement, as well as two possible endings.
You find a locked safe midway through Depth 4. A hint for the code can be found on its side.
In case you miss them, here is what to look for in the surrounding area:
If you can not figure it out, the code is: 5837. Besides its own achievement, unlocking the safe and picking up the contents is crucial for obtaining another three.
As soon as you drop down a slope in Depth 5, check the right side for a small opening. This path leads to the mask but you require something for stepping on to get across the gap on the way. Go through the 'tunnel of doors' and reach the area with fenced compartments. Search the area to find a plank.
Make your way back to the opening, place the plank on the gap and get to the the other side. Use the fire axe to tear down the wooden barrier.
Place three sticks of dynamite on the box follow the on-screen instructions to detonate them. Further explore the place after the detonation to find the gas mask.
Be sure to equip the mask through the inventory screen as soon as you pick it up to avoid further contamination. Just as the axe that can be found in Depth 4 is required to get to the gas mask, the mask itself is also a must as you descend to Depth 6 (if you are aiming for either the second or the third ending).

A maximum of 7 dynamite sticks, 8 golden coins and 3 blood trees can be collected throughout the game. Listed below are all the collectibles in order of appearance:
1) Depth 1, a stick of dynamite can be found in the cabinet next to barrel with the shack storage key on it.
2) Depth 2, another stick of dynamite can be found in a cabinet on your way down to Depth 3, if you choose to descend by way of the route within the cave. (This route is not recommended.)
3) Depth 3, just as you come to your senses, turn back to find the first blood tree lying on the floor. Note that this area is only reachable if you choose to drop down into the pit in Depth 2. (This is the recommended route.)
4) Depth 3, after picking up the blood tree follow the path upwards to find a golden coin and a stick of dynamite on a couple of boxes. Likewise, these two are only reachable if you choose to take the 'pit route' in Depth 2.
5) Depth 3, a stick of dynamite and a golden coin can be found on top of a box lying near a bunch of trees.
6) Depth 3, another stick of dynamite and yet another golden coin can be found in a cabinet that is only unlockable if you have five valid shots by this point.
7) Depth 4, two golden coins can be found on a couple of barrels.
8) Depth 4, another golden coin can be found lying next to the 'device'.
9) Depth 4, a couple of coins, a stick of dynamite and the second blood tree can be found in the locked safe which is tied to a puzzle.
10) Depth 4, another stick of dynamite can be purchased for six golden coins from the dispenser found right next to the locked safe. Might as well if you have the coins, since they are not usable anywhere else.
11) Depth 5, the last stick of dynamite can be found in the area with fenced compartments.
12) Depth 5, still in the same area, there is a cabinet that is only unlockable if you have twenty valid shots by this point. The third and the final blood tree is to be found inside.

Since the game does not save your progress at all, three runs are needed to get all the endings.
Reaching Depth 6 without an equipped gas mask or already being fully (100%) contaminated before equipping the said mask results in the first (Sickened) ending.
Only having a gas mask equipped lets you explore Depth 6 further.
Coming upon a couple of elevators, you can either:
take the right one to ascend back to Depth 1, which results in the second (Defeated) ending,
or take the left one to descend to Depth 7, which results in the third (Adventurous) ending.

There are also two secret endings, as discovered by turbomaxou.

Secret Ending 1 (Fatal): Ascend back to Depth 1 (as in the second ending) under 30 minutes.
Secret Ending 2 (Magical): Unlock the sealed door found in Depth 1 (details in the next section).

(Once again the credit goes to turbomaxou.)

Although not tied to an achievement, you may notice that the stats screen that comes up at the end of every run mentions an easter egg. If you want to access it, be sure to collect all three blood trees and the gas mask on your way down to Depth 6. Take the elevator down to Depth 7 (as in the third ending), pick up the access card but do not use it on the gate. Instead, take it all the way up to Depth 1. The sealed door with the symbols on it opens up as you approach, allowing you to explore further. On a side note, taking this path also results in the second secret ending (Magical).